(a) Technical Field
The present invention relates to a gasket structure of a fuel cell separator with an improved air tight seal. More particularly, it relates to a gasket structure of a fuel cell separator, which can an improve air tight seal of flow channels without occurrence of a gasket burr and facilitate flow of fluid in each flow channel, by forming a vacant space on a gasket formed integrally with the fuel cell separator.
(b) Background Art
Generally, a metal separator manufactured by a method of, for example, stamping a thin metal plate has an advantage of significantly reducing the manufacturing time and cost compared to a graphite separator manufactured by mechanical working or powder molding. In a fuel cell in which a plurality of metal separators are stacked in series, a gasket is disposed between the metal separators, and the gasket may be integrally manufactured on both surfaces of the separator by an injection molding method. In this case, since the fuel cell that has to maintain an air tight seal of reactant gases and cooling fluids, the gasket has to be manufactured to maintain the air tight seal of working fluids.
An exemplary fuel cell separator having a gasket for maintaining an air tight seal has been previously disclosed in Korean Patent Application Publication No. 10-2011-0015924, filed by the present applicant, and is hereby incorporated by reference.
As shown in the above disclosure, a gasket is fuel cell assembly is integrally injection-molded on the separator. Gaskets integrally injected on both surfaces of a separator are continuously connected to form a closed curve. Also, a plurality of injection apertures are formed at all edges of the separator and boundary surfaces between manifolds to allow a gasket injection fluid to pass through. The gasket injection fluid flows from one surface to the other surface of the separator through the injection apertures, integrally injection-molding the gaskets on both surfaces of the separator.
More specifically, the structure of a gasket integrally formed on a reaction surface side and a cooling surface side of a typical separator shown in FIGS. 1A and 1B, respectively, will be described below. A reaction surface 10 of a separator shown in FIG. 1A is a location/area where a fuel cell reaction occurs. Manifolds 20, 22 and 24 serve as passageways for hydrogen, cooling water, and air, and are located at the reaction surface 10. A reaction surface side main line 30a is formed at the side of the reaction surface 10 by injection molding to interrupt movement of reactant gases and cooling fluids. A plurality of sub lines 32a parallelly extend from the main line 30a at a certain interval as shown in FIG. 1A. Hydrogen introduced from the side of the cooling surface 12 (described later) moves to the reaction surface 10 through the hydrogen passageway 40.
Also, a cooling surface 12 of the separator shown in FIG. 1B is a portion for removing reaction heat generated by the chemical reaction. The manifolds 20, 22 and 24 that serve as passageways for hydrogen, cooling water, and air are located at the cooling surface 10. A cooling surface side main line 30b is formed on one side of the reaction surface 10 by injection molding so that air is interrupted, but cooling fluid and hydrogen are introduced respectively.
A plurality of sub lines 32b parallelly extend from the main line 30b at a certain intervals as shown in FIG. 1B. Hydrogen introduced from the side of the cooling surface 12 (described later) moves to the reaction surface 10 through the hydrogen passageway 40. A detailed description of flow of cooling water, hydrogen and air in the flow channel and other components of the separator will be omitted herein.
The gasket manufactured by a typical injection molding method has a limited amount of airtightness. These limitations will be described below with reference to FIGS. 2A and 2B. FIG. 2A is a view illustrating the structure of a gasket integrally formed on a typical separator, and FIG. 2B is a cross-sectional view of a mold for manufacturing a gasket formed along line A-A of FIG. 2A.
In FIG. 2A, a gasket indicated by a solid line is a main line 30a and a sub line 32a on the side of the reaction surface, and a gasket indicated by is a main line 30b and a sub line 32b on the side of the cooling surface, i.e., on the opposite surface of the separator. In this case, a region where the reaction surface side gasket 30a and 32a and the cooling surface side gasket 30b and 32b are installed includes regions 50 and 54 where the gasket is disposed on different lines and a region 52 where the gasket is disposed on the same line.
Among the above regions, the region 52 where the gasket is disposed on the same line and a cooling fluid flows in and out is manufactured by an upper gasket mold 60a and a lower gasket mold 60b that are disposed based on the separator as shown in the upper figure of FIG. 2B. Since substantially uniform injection pressures P1 and P2 act on the both molds, any limitation does not occur in gasket injection.
However, the regions 50 and 54 where the gasket is not disposed on the same line and reactant gases flows in and out is manufactured by an upper mold 60a′ and a lower mold 60b′ that are disposed based on the separator as shown in the lower figure of FIG. 2B. The magnitude of an injection pressure P1′ becomes greater than the magnitude of an injection pressure P2′ due to an intaglio structure difference between both molds according to the shape of the gasket. Thus, since different injection pressures are locally applied, a pressure applied in the arrow direction as indicated in the lower figured of FIG. 2B causes a minute deformation of the separator and thereby causing the gasket to burr.
The deformation of the separator and the burr of the gasket mean the vicinity of the gate of reactant gases cannot be uniformly compressed upon coupling of a fuel cell stack, and a considerable portion of fuel cell stack may as a result be poorly sealed. Furthermore, the burr generated at the gate region of reactant gases results in the gasket being exposed to a hot and humid environment created by operation of a fuel cell. Since the gasket is formed of a polymer material and is vulnerable to temperature and moisture, the gasket manufactured by a typical method as shown in FIG. 3 may be easily exfoliated and expanded from the surface of the separator. As a result, the flow of reactant gases may be hindered, and the water discharging capacity may be reduced, causing the rapid reduction of the performance and the durability of the fuel cell.
Accordingly, when the gasket is integrally formed on the surface of the metal separator by a typical method, particularly, by injection molding, minute deformations of the separator and burrs in the gasket may occur.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.